1. Field of the Invention
The present invention relates to an optical disc device that can record information in an optical disc and reproduce recorded information from the optical disc, and a method for recording optical information.
This application claims the priority of Japanese Patent Application No. 2004-330991, filed on Nov. 15, 2004, and Japanese Patent Application No. 2005-219487, filed on Jul. 28, 2005, in the Japanese Patent Office, the disclosure of which are incorporated herein in its entirety by reference.
2. Description of the Related Art
A variety of writable optical recording mediums are commercially available which allow users to record large amounts of information. Examples include write once read memory (WORM) type optical discs, such as CD-R discs, and rewritable type optical discs, such as CD-RW discs. More recently, high-capacity digital video discs (e.g., DVD-R, DVD-RW and DVD-RAM) have been introduced as the result of the use of shorter wavelength laser beams, decreased spot diameters, and thin substrates. Generally, data is recorded in the form of non-reflective marks along a spiral track of the optical discs. Herein, the term “mark” refers to the pit, spot or region along the track in which data of a given logic value (e.g., “1”) is recorded along the track. For example, the marks may be formed as non-translucent dye regions in the case of CD-R discs, or as amorphous regions in the case of CD-RW discs. The spaces located between the marks along the spiral track are often referred to as “lands”. The lands are typically formed as translucent dye regions in the case of CD-R discs, and as polycrystalline regions in the case of CD-RW discs.
In order to avoid extended gaps (which can cause tracking problems) where there are no marks in the data track of a compact disc, data is typically encoded using “Eight to Fourteen Modulation” (EFM). In EFM, 8-bit bytes are converted to 14 bits, with at least some of the 14 bits being logic “1” (marks). However, variations in physical characteristics among optical discs can result in improper recording of the EFM signal. That is, mark formation failures can occur for a variety of reasons, such as variations in the composition of the dye recording layer of the optical disc, and heat accumulation of the recording media coupled with an insufficient cooling rate. In other words, the writer parameters that might be best suited for one optical disc may not be ideal for another optical disc.
As such, in an effort to improve write accuracy, a reference write pattern is used to determine and set optimal or preferred write parameters of an optical disc to be recorded in advance of a recording operation. Herein, the set write parameters associated with an optical disc are referred to as a “write strategy” of the optical disc. It is known that this write strategy is closely related with a number of factors, including recording rate, dye material, phase-change material, dye film thickness, track configuration, and so on.
The write strategy generally defines or sets a number of variable write conditions of the optical disc. For example, the mark-to-land ratio may be varied, an additional pulse may be added to the front end of a write pulse, the rise or fall position of a write pulse may be altered, a write pulse may be converted to a multi-pulse format, and so on.
A mark is generated by irradiating a short pulse onto the optical disc at a high recording power. By varying the mark-to-land ratio it is possible to provide a good shape for the front end and rear end of the mark, by shortening the length of the mark during a low speed recording.
Adding an additional pulse to the front end of a recording pulse enhances the shape of the front end, which is formed by additively applying a recording power to the front end of the mark that is hard to deform by heat due to irradiation of the laser.
Changing the rise or fall position of a recording pulse by a combination of the mark and land can make uniform the length of the mark and land. When the mark and land are formed, the position of the front end of the land is adjusted according to the distance to the rear end of the land because the heat from creating any mark will also influence a subsequent mark. So the position of any land is changed or the heat for recording the front of the mark is transferred to the land in front of a mark according to the length of the land in front of the mark, and the rear position of the mark is changed or the heat for recording the rear end of the mark is transferred to the land behind the mark to influence the land behind the mark, according to the length of the recording mark.
The method of converting a recording pulse into a multi-pulse format is mainly used for a phase change disc, such as a CD-RW, or a DVD. When recording information in a phase change disc using a successive pulse, heat generated during the recording operation erases the front end of the recorded information. To solve the above erase problem, a multi-pulse having a cooling period between recording pulses is used.
Also, since there exist in the market too many kinds of optical discs so that manufacturers cannot be aware of and account for all of them completely, it is impossible to prepare a proper write strategy in advance for all optical discs in the market.
Due to the above problem, a method of recording information while varying a write strategy into two or more tracks in an optical disc area and selecting a write strategy for which reproduction jitter is minimized (e.g., Japanese Patent Publication No. 2000-30254), and a method of recording information using a specific record pattern, and obtaining a combination of marks and lands by which a jitter value or a deviation value is minimized (e.g., Japanese Patent Publication No. 2003-30837), are proposed.
However, in the method disclosed in Japanese Patent Publication No. 2000-30254, a finally selected write strategy is only the best write strategy among the predetermined set of write strategies, and is not the optimal write strategy for an optical disc in use. In addition, this method is problematic in that tracks are used as a record area necessary for a test.
Also, in the method disclosed in Japanese Patent Publication No. 2003-30837, since a particular pattern is used and an influence on a mark or a space other than when changing the particular mark or space is not sufficiently considered, it is very difficult to set an optimal write strategy for an optical disc in use.
Further, in recording information on a DVD-RW, it is problematic in that a regulation recommends that different writes strategies be used for the case of an even T than for the case of an odd T. Also, it is problematic that too many parameters are used in order to set such write strategies. Further, it is difficult to set such write strategies.